1. Field of the Invention
The present invention relates to copper precursor compositions and their synthesis, and to a method for fabricating copper-containing microelectronic device structures such as in formation of metal interconnects for the manufacture of semiconductor integrated circuits, or otherwise for metallizing or forming copper-containing films on a substrate by metalorganic chemical vapor deposition (MOCVD) utilizing such precursor compositions.
2. Description of the Related Art
The process of fabricating semiconductor integrated circuits generally includes the formation of metal interconnect lines. The metal interconnect lines often may be formed from multiple conductive layers. For example, a thin conductive layer generally termed a barrier layer may be formed from a metal or metal suicide and a thicker conductive layer formed from a conductive material, for example aluminum, may be formed on the barrier layer.
In order to enhance circuit speed performance and reduce electro-migration effects, the use of copper layers has been proposed to replace the use of aluminum layers. Thus one or more metal layers of a semiconductor integrated circuit may be formed utilizing a copper-based layer. Copper is of great interest for use in metallization of VLSI devices because of its low resistivity, low contact resistance, and ability to enhance device performance through the reduction of RC time delays. Many semiconductor device manufacturers are adopting copper metallization for use in production of microelectronic chips.
Chemical vapor deposition (CVD) is a potentially useful technique for metallization in the fabrication of microelectronic device structures, e.g., liquid delivery metalorganic chemical vapor deposition (MOCVD), wherein liquid precursor material is introduced to a vaporizer unit including a heated vaporization element and volatilized at high rate ("flash vaporized") in contact with the heated vaporization element to form a precursor vapor. The precursor vapor then is contacted with a substrate at sufficient elevated temperature to deposit a metal-containing film on the substrate from the precursor vapor.
Liquid delivery MOCVD is a highly useful technique for formation of metal-containing films on substrates. In application to metallization in microelectronic device structures, the accuracy and precision of the delivery rate of precursor in liquid delivery MOCVD that is achievable using volumetric metering and other monitoring and process control aspects of liquid delivery MOCVD technology, in turn enables commercial reproducibility to be attained in the metallization operation for very large scale integration (VLSI) device manufacture.
Liquid delivery MOCVD, however, requires liquid precursor compositions. Such compositions may comprise source reagent compounds or complexes that are themselves liquids, or alternatively the precursor composition may comprise compounds or complexes that are dissolved or suspended in a suitable liquid solvent medium. Advantageous liquid precursor compositions are desirably stable at ambient temperature (e.g., in the range of 10-40.degree. C.) conditions, for extended periods of time, to accommodate transportation and storage of such compositions subsequent to their manufacture and prior to their use.
Although the use of copper precursors in MOCVD to create copper interconnects in semiconductor integrated circuits is known (see, e.g., U.S. Pat. Nos. 5,085,731; 5,098,516; 5,144,049; and 5,322,712; and the references cited therein), only a few liquid copper precursors are commercially available. These include (hfac)Cu(MHY), (hfac)Cu(3-hexyne), (hfac)Cu(DMCOD) and (hfac)Cu(VTMS), wherein hfac=1,1,1,5,5,5-hexafluoroacetylacetonato, MHY=2-methyl-1-hexen-3-yne, DMCOD=dimethylcyclooctadiene, and TMVS=trimethylvinylsilane.
New and useful compositions and processes for the production of copper that improve on, or provide alternatives to, these known compositions would be highly desirable for large-scale manufacture of integrated circuits, including formation of copper on the microelectronic device substrate (i) as a conductive thin-film plating base layer for subsequent electroplating of metal thereon, and/or (ii) in so-called "full-fill" deposition of copper for forming interconnects and other elements of microelectronic device structures.
In the first such application, of forming a copper film plating base, or seed layer, for subsequent electroplating, the copper film must have low resistivity and uniform thickness, to achieve uniform current density in the electroplating operation. The copper film also must be of a uniform conformability character to accommodate the high aspect ratio features, complex geometries and damascene processing involved in VLSI device manufacture. Finally, the copper film must have excellent adhesion to the barrier layer.
The copper precursor currently most widely used in semiconductor device manufacture is the aforementioned (hfac)Cu(TMVS), commercially available as CupraSelect (Schumacher Division of Air Products & Chemicals, Inc., Allentown, Pa.). This precursor, however, suffers from inherently poor thermal stability and therefore requires additives to enhance the molecule's physical properties, including thermal stability, and to facilitate uniform nucleation and film growth.
By way of example, Norman et al. U.S. Pat. No. 5,322,712 teaches that improved quality copper films are produced in the MOCVD usage of (hfac)Cu(TMVS) when a volatile ligand or ligand hydrate, e.g., hexafluoro-2,4-pentanedionate hydrate is introduced into the CVD reactor with vapors of the (hfac)Cu(TMVS) precursor. The Norman et al. patent does not describe the use of a liquid delivery flash vaporization technique in connection with the precursor compositions therein disclosed. Instead, the patent teaches to employ a low pressure evaporation chamber to evaporate the ligand or ligand hydrate under reduced pressure, with the (hfac)Cu(TMVS) being volatilized in a bubbler or the same type low pressure evaporation chamber as the ligand or ligand hydrate.
The additives disclosed in the Norman et al. patent, however, may lead to contamination of the copper film, either during nucleation or steady-state film growth. In both cases, the electrical properties of the film may be compromised, resulting in high film resistivity and/or high contact resistance. In multi-layered structures, such electrical properties are critical to device integration and manufacture.
Such contamination of the product film incident to the use of the ligand or ligand hydrate as additives in accordance with the Norman et al. patent is attributable to the fact that the ligand is susceptible to decomposition during the film growth process, especially at the barrier-copper interface. In addition, over time precursors such as (hfac)Cu(TMVS) show decomposition to green Cu(II) species. These are significant deficiencies of the prior art.
The prior art (in N. Awaya, et al., Conf. Proc. ULSI-VII 1992 MRS, p.345) has disclosed that water vapor can accelerate the deposition of copper from CVD precursors, and the aforementioned Norman et al. patent discloses the addition of 50 ppm of water vapor to pure, dry (hfac)Cu(TMVS) under oxygen-free CVD conditions to show the resultant formation of Hhfac. Such steam injection operation of the MOCVD system, however, requires a separate boiler and feed water source as well as associated injection means, and increases the cost and complexity of the MOCVD process system.
There is therefore a need in the art for new and improved copper precursor compositions and methods for use in the manufacture of integrated circuits and other microelectronic device structures, using techniques such as chemical vapor deposition, plasma-assisted CVD, etc., and particularly liquid delivery MOCVD.
It is accordingly an object of the present invention to provide new copper precursors.
It is another object of the invention to provide a method of depositing copper in the manufacture of integrated circuits and other microelectronic device structures, utilizing such copper precursors.
It is a further object of the invention to provide metallization precursor compositions and methodology for forming interconnects and other device structures, which overcome the shortcomings and limitations of the prior art.
Other objects and advantages of the present invention will be more fully apparent from the ensuing disclosure and appended claims.